The overall objective of this project is to develop in vitro methods to the point that biochemical techniques could be used in the analysis of mutants which block imaginal disc development in Drosophila melanogaster. We have recently formulated a new medium and are evaluating its ability to support the growth of imaginal discs in vitro. One or more enzymes specifically localized in imaginal discs are absent in discs from a temperature-sensitive mutant. We are studying regulation of such enzymes in mutant discs differentiating in vitro.